1. Field of the Invention
This invention relates to an orthodontic bracket useful in correcting irregularities in alignment of teeth.
2. Description of the Related Arts
To treat patients troubled with irregularities in alignment of teeth, plural orthodontic brackets, made of metals and resins etc., are usually used. Each orthodontic bracket has a bracket body having, on its upper surface, wire slots adapted to hold an arch wire across the upper surface of the bracket body. Each orthodontic bracket is bonded with an adhesive to a surface (a front surface in the case of an incisor, or a side surface in the case of a molar) of each tooth to be repositioned.
For bonding each orthodontic bracket to a tooth side surface, the bracket position is set with respect to the tooth such that the bracket body's center line and the tooth center line are in alignment with each other and that the arch wire held with the wire slots of each orthodontic bracket is arranged linearly in parallel with a linear occlusal plane of the teeth to be obtained by orthodontic treatment. Then, each orthodontic bracket is bonded to set the bracket position for each tooth.
With the arch wire held in the wire slots of each orthodontic bracket placed on corresponding tooth side surfaces as described above, the orthodontic brackets are connected together through the arch wire. Then, insertion of the opposite ends of the arch wire into respective buccal tubes united with more distal teeth is performed with the arch wire under tension followed by connection of the arch wire to the respective buccal tubes.
With each orthodontic bracket placed on a corresponding tooth side surface as described the above, the orthodontic treatment is effected by the elastic recovery force of the arch wire to provide distal movement (movements from the incisor side toward the molars) or mesial movement (movement from the molar side toward the incisors) of each tooth requiring realignment, or alternatively, to adjust occlusion between upper and lower teeth and to eliminate torsion.
The orthodontic treatment may be applied after extraction of a tooth to eliminate crowding or without extraction. However, as is obvious from the above description, in either case, setting of the bracket position is quite important in order to bond each orthodontic bracket in proper position on a tooth.
Some important problems involved in bonding of each orthodontic bracket include positioning and/or orienting the bracket body so that the wire slot in the bracket body and the linear occlusal plane of teeth are parallel, positioning and/or orienting the bracket body for alignment between the bracket body and the corresponding tooth, and matching the contour of the bracket body to the corresponding tooth side surface.
To solve the above problems, Japanese Patent Laid-open No. 8-112293, for instance, discloses an orthodontic bracket having a bracket body having, at its opposite sides, a pair of tie-wings each having a central wire slot formed across it. Each tie-wing has a first visible reference line on its median, parallel to a longitudinal axis of the tooth, and each wire slot has, on its axis intersecting the first visible reference line, a second visible reference line parallel to a linear occlusal plane of the teeth. The orthodontic bracket of this type allows bonding to the corresponding tooth side surface with the adhesive using the first and the second visible reference lines, permitting the bracket to be bonded in its proper position in accordance with the longitudinal axis of each corresponding tooth and with the linear occlusal plane of the teeth.
Japanese Patent Laid-open Application No. 2005-192989 discloses an orthodontic bracket having a mark on a contour line extending from a longitudinal center line located on a bottom surface of each wire slot of the bracket body and defined by intersection of a plane perpendicular to the bottom surface of each wire slot with the surface of the bracket body. The orthodontic bracket of this type provides for alignment of the mark with a mid-transverse plane of the tooth to be bonded to the bracket and provides a bracket base point on the mid-transverse plane, thus locating the bracket accurately on the tooth.
However, the orthodontic bracket, even after accurate positioning of the each tooth brings about distal or mesial movements of the tooth to be corrected, with advance of the orthodontic treatment depending on clamping force of the arch wire, causes in a change in occlusion between the upper and lower teeth. Thus, the conventional orthodontic brackets cause a change in occlusion of the teeth with the advance of the orthodontic treatment, which change necessitates a change of bracket position setting. Thus frequently resetting of the bracket body of the arch wire is required, prolonging the time required for the orthodontic treatment, and imposing a heavy burden upon the patients.